A principal objective of the proposed program is to evaluate the role of furocoumarin complexing to DNA on the pathway of the initial photosensitized reactions. The quantum yields for the formation of furocoumarin monoadducts and DNA cross-links are being measured for different conditions of equilibrium complexing. The photooxidation of DOPA to dopachrome is being investigated, in connection with the molecular mechanism of the "tanning" reaction in PUVA therapy. New work will be initiated on liposome damage photosensitized by furocoumarins as mediated by complexing to DNA. The current liposome studies on the attack of singlet oxygen and superoxide on the membrane will be continued emphasizing the effect of lipid composition on the efficiency of lysis by these agents. The results will be analyzed with the "large target" theory making it possible to relate the dose-response data to kinetic events at the liposome surface.